This study is a follow-up of previous studies conducted by the NIDR in Illinois in 1980 and 1985 and in Iowa in 1982 to assess the prevalence of dental fluorosis and dental caries among schoolchildren exposed to different concentrations of fluoride in their drinking water. Both Illinois surveys were carried out in the same communities, which had naturally occurring fluorides in their water supplies at concentrations of approximately one, two, three and four times that recommended as optimal for those areas. In contrast, the Iowa communities had negligible concentrations of fluoride in their drinking water. The need to monitor for possible changes in the prevalence of dental fluorosis continues to receive high priority. Additional research also is needed to further elucidate and define current interrelationships between dental caries, dental fluorosis, and various concentrations of fluoride in drinking water. The continued availability of the same communities in Illinois and the identification of two communities in Nebraska with negligible concentrations of water-borne fluoride have afforded an excellent opportunity to address these research needs. Examinations were completed in April 1990 on approximately 300 schoolchildren ages seven through 16 in the two Nebraska communities. Each child was examined for dental caries using the DMFS index and for dental fluorosis using both Dean's Index and the Tooth Surface Index of Fluorosis. Examinations, using the same indices, were conducted in October 1990 in Illinois. Data from all study sites currently are being analyzed.